Locally based Captain D's has restaurants in 22 states, most of them in the Southeast. Out of its total number of units, 317 are company-operated and the rest are franchised. Ronald D. Walker, Captain D's president and COO, will continue to lead the chain.

This is not the first restaurant venture for Boston-based Charlesbank. The firm also owns interests in Papa Murphy's, a carryout pizza chain with about 825 stores across the country. It also has interests in Canadian drugstore chain Shoppers Drug Mart.

Timonium, MD-based Grotech invests in companies in a variety of different industries, including healthcare, software and communications infrastructure. Grotech's retail-related holdings have included interests in Yorkshire, the former owner of A&W and Long John Silver's restaurants, as well as Minneapolis-area online grocery delivery service Simon Delivers.